/in/foo.c: In function 'main':
/in/foo.c:8:9: error: incompatible type for argument 1 of 'sqrt'
  r=sqrt("a*2+b*2")
         ^~~~~~~~~
In file included from /usr/include/features.h:364:0,
                 from /usr/include/stdio.h:27,
                 from /in/foo.c:1:
/usr/include/x86_64-linux-gnu/bits/mathcalls.h:156:1: note: expected 'double' but argument is of type 'char *'
 __MATHCALL (sqrt,, (_Mdouble_ __x));
 ^
/in/foo.c:9:2: error: expected ';' before 'printf'
  printf("r")
  ^~~~~~
/in/foo.c:6:13: warning: variable 'r' set but not used [-Wunused-but-set-variable]
     int a,b,r;
             ^